This invention relates to an apparatus for heating a carbonaceous material to produce a gas, and more particularly to an apparatus for regenerating a saturated char to produce a stream of high sulfur dioxide concentration.
Hydrocarbon fuels, which are normally burned in industrial installations, such as coal and oil-fired power stations, contain sulfur which, under normal circumstances, is converted to sulfur dioxide in the combustion process. Although in older installations the sulfur dioxide was vented to atmosphere with the other effluent gases from the process, recent air pollution control requirements have placed great emphasis on removing the sulfur dioxide from the gases before the latter are expelled into the atmosphere. One successful technique in this respect is to remove the sulfur dioxide from polluted gas streams by adsorption on carbon to form a saturated char followed by a regeneration of the saturated char to produce a stream of high sulfur dioxide concentration.
The regeneration of the saturated char is often accomplished by thermal regeneration, in which the saturated char is contacted with an inert, head exchange medium, such as sand, which has been heated to a predetermined elevated temperature. The sand does not take part in the reactions occurring within the regenerator, but rather simply functions to supply heat so that the reactions may take place. As the char becomes heated, the reactions that occurred during the adsorption process are reversed, producing a concentrated stream of sulfur dioxide, water, carbon dioxide and nitrogen.
In a typical regeneration process the mixture of the hot sand or heat exchange medium and the char flows slowly down through the regeneration vessel, with the flow being controlled by a char-sand separator/feeder positioned below the discharge hopper of the vessel.
With this type of thermal regeneration, a regeneration temperature with a high, heating velocity can be achieved. This results in a regeneration vessel of small volume and a short char residence time.
In this regeneration process the sulfur dioxide rich gas normally is drawn out by an induced draft fan through an outlet opening formed in the upper portion of the reactor vessel. However, in these arrangements some of the sand, or other heat exchange medium, is sometimes fluidized by the gas and hence carried out of the regenerator through the outlet opening. This of course reduces the efficiency of the system in addition to requiring external separation of the sand and addition of new sand to the system.